Lens plate, method for manufacturing the same and image transfer device

ABSTRACT

Spherical convex micro-lenses are arranged between rectangular grooves adjacent to each other of a lens plate. The arrangement of convex micro-lenses is made to be in parallel with the short-side direction of the lens plate, namely, the direction of the rectangular grooves. Since stray light appears mainly on the convex micro-lenses arranged in the long-side direction of the lens plate, the stray light to appear in the long-side direction of the lens plate is removed by forming grooves at regular intervals in the long-side direction of the lens plate and forming a light absorbing film in each of the rectangular grooves. Or the stray light to appear in the long-side direction of the lens plate is removed by making the direction of arrangement of convex micro-lenses different from the long-side direction of the lens plate.

This application is a divisional of U.S. application Ser. No.10/878,580, filed Jun. 28, 2004 now U.S. Pat. No. 7,116,484, the entirecontents of which are hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lens plate capable of removing straylight, a method for manufacturing the same and an image transfer devicefor transferring an image to a linear image formation area using anerecting lens array formed by combining lens plates.

2. Description of the Related Art

An optical system of a device for reading an image includes a reducingsystem and a unit magnification system. A lens array to be used in aunit magnification system is an erecting unit magnification lens arrayand ordinarily has several rows of rod lenses defined herein as lensrows arranged along a long-side direction of the lens array (in amain-scanning direction of an image reading device). Although it ispossible to improve the transferability of a light quantity and reducean unevenness in quantity of transmitted light by increasing the numberof rows of lenses, the number of lens rows, in general, is one factor inconsideration of a manufacturing cost for a lens array using rod lenses.

On the other hand, an erecting unit magnification lens array can also beformed using a resin lens plate having a plurality of convexmicro-lenses arranged on its surface. A lens array using such a resinlens plate provides an advantage of enabling a lens array having aplurality of lens rows to be manufactured at a comparatively low cost.

However, since an erecting unit magnification lens array using aconventional resin lens plate does not have a wall for shading a lightbeam between lenses adjacent to each other, there is a problem of straylight that a light beam obliquely entering a lens plate obliquelyproceeds through the plate, enters an adjacent convex lens and thenexits the lens to form a ghost image.

There are known methods to counter such stray light. One method of formsa light shading layer between adjacent lenses. A method forms a lightshading layer between lens plates arranged opposite to each other. Alight shading layer may be formed by means of a photolithography processusing a photoresist containing a light absorbing agent. Another methodforms a light shading layer by applying a light absorbing paint to thewhole surface of a lens face and removing only the light absorbing painton the lens part. A further method forms a light shading layer byapplying a light absorbing paint to a part on which a light shadinglayer is to be formed by means of an ink-jet printing method. Anothermethod forms a light shading layer by forming a groove in a part onwhich a light shading layer is to be formed and filling this groovewith, for example, a light absorbing paint.

The formation of light shading layers around lenses, between adjacentlenses and between lens plates arranged opposite to each other iseffective for removing light coming in from outside of a lens area orremoving light obliquely entering a lens and exiting from the outside ofa lens area. However, the light shading layers cannot remove stray lightformed by light obliquely entering a lens, passing through a lens platein the direction of a thickness of the lens plate and exiting from theexit side of a lens adjacent to that lens.

In the case of forming a light shading layer by forming a groove andfilling the groove with a light absorbing paint, the groove may beformed by means of a transfer molding method using a metal mold. A lightshading film may be formed on side faces and a bottom face of thegroove. The depth of the groove is limited by the formability of a lensshape or the releasability of a lens plate from the metal mold.Therefore, it is difficult to obtain a groove having an aspect rationecessary for forming a light shading layer necessary for removing straylight formed by light obliquely entering a lens, passing through a lensplate in the thickness direction of the lens plate and exiting from theexit side of a lens adjacent to that lens.

Therefore, an erecting unit magnification lens array using aconventional resin lens plate still has a problem in that it cannotsufficiently remove stray light, makes a ghost image and is inferior inresolution.

An object of the present invention is to provide an erecting lens arraycapable of sufficiently removing stray light.

Another object of the present invention is to provide an image transferdevice capable of sufficiently removing stray light in using an erectinglens array.

SUMMARY OF THE INVENTION

A first aspect of the present invention is a lens plate comprising arectangular plate having a plurality of grooves formed in the plate to aspecific depth at specific intervals in parallel with one another in theshort-side direction of the plate, a plurality of lens rows of convexmicro-lens formed with said grooves between them at specific intervalsin parallel with one another in the short-side direction of the plate,and light absorbing films formed in said grooves. Said grooves each areformed to a depth of ⅓ or more of the thickness of said plate.

A second aspect of the present invention is a method for manufacturing alens plate comprising the steps of molding a rectangular plate having aplurality of grooves formed to a specific depth at specific intervals inparallel with one another in the short-side direction of the plate,forming in the plate a plurality of lens rows of convex micro-lenseswith said grooves between them at specific intervals in parallel withone another in the short-side direction of the plate, and forming lightabsorbing films in said grooves. The convex micro-lenses are formed onthe plate by a hot-embossing method.

A third aspect of the present invention is an image transfer deviceusing an erecting lens array formed by combining two or more lens platesas described above.

A fourth aspect of the present invention is an image transfer device fortransferring an image to a linear image formation area, comprising alight source, and an erecting lens array being at least provided with afirst lens plate being rectangular and arranged at the light entranceside and having a lens formation area in which convex micro-lenses areregularly arranged at intervals of specified lens pitch on at least oneface of it and a second lens plate being in the same shape as the firstlens plate and arranged at the light exit side, said erecting lens arraycontaining the whole of one or more of said convex micro-lenses in alight beam input enabling area (in a possible area of light incidence)in the first lens plate of a light beam outputted from said lightsource.

The direction of arrangement of convex micro-lenses and the long-sidedirection of a lens formation area are not the same as each other. Theother areas than portions functioning as lenses have light absorbency onone or both faces of at least one lens plate, light absorbing walls forremoving unnecessary light beams are provided between convexmicro-lenses at least on one lens plate, and grooves for removingunnecessary light beams are provided between convex micro-lenses on oneor both faces of at least one lens plate.

And the direction of arrangement of convex micro-lenses and thelong-side direction of a linear image formation area are not the same aseach other. In case that the arrangement of convex micro-lenses is ahexagonal arrangement in which lenses are hexagonally arranged, thedirection of a line tying the centers of lenses and the long-sidedirection of a linear image formation area are not the same within acircular area having a length of two times the lens pitch as its radiusand one convex micro-lens as its center. In case that the arrangement ofconvex micro-lenses is a rectangular arrangement in which lenses arearranged in the shape of a matrix (in a grid), the direction of a linetying the centers of lenses and the long-side direction of a linearimage formation area are not the same within a circular area having alength of ((long pitch)²+(short pitch)²)^(1/2) as its radius and havingone convex micro-lens as its center.

And the erecting lens array is provided with a slit-shaped opening forremoving unnecessary light beams within the object point side workingdistance and/or the image point side working distance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing a lens plate according to the presentinvention.

FIG. 2 is a sectional view taken along line A—A of FIG. 1.

FIG. 3 shows a plan view and a side view showing a resin plate formed byan extrusion molding method.

FIG. 4 shows a plan view and a side view showing a resin plate havinglight absorbing films formed in rectangular grooves.

FIG. 5 shows a plan view and a side view showing a large-size lens platehaving convex micro-lenses formed on both faces of it by a hot-embossingmethod.

FIG. 6A is a partial magnified sectional view of a resin plate beforelens rows are formed in the resin plate by a hot-embossing method.

FIG. 6B is a partial magnified sectional view of a resin plate afterlens rows have been formed in the resin plate by a hot-embossing method.

FIG. 7 shows a plan view and a side view showing a large-size lens platehaving a black resist applied to it.

FIG. 8 shows a plan view and a side view showing a large-size lens platebeing in a state where it has been cut.

FIG. 9A is a plan view showing an example of an image transfer deviceusing lens plates according to the present invention.

FIG. 9B is a sectional view taken along line B—B of FIG. 9A.

FIG. 9C is a bottom view showing the image transfer device shown in FIG.9A.

FIG. 9D is a sectional view taken along line C—C of FIG. 9A.

FIG. 10A is a plan view showing another example of an image transferdevice using lens plates according to the present invention.

FIG. 10B is a sectional view taken along line D—D of FIG. 10A.

FIG. 10C is a bottom view showing the image transfer device shown inFIG. 10A.

FIG. 10D is a sectional view taken along line E—E of FIG. 10A.

FIG. 11A is a plan view showing a further example of an image transferdevice using lens plates according to the present invention.

FIG. 11B is a sectional view taken along line F—F of FIG. 11A.

FIG. 11C is a bottom view showing the image transfer device shown inFIG. 11A.

FIG. 11D is a sectional view taken along line G—G of FIG. 11A.

FIG. 12A is a variation example of an image transfer device.

FIG. 12B is a variation example of an image transfer device.

FIG. 13 is a plan view showing a lens plate for forming an erecting lensarray according to the present invention.

FIG. 14 is a sectional view taken along line H—H of FIG. 13.

FIG. 15A is a figure showing a state of forming the image of a pointlight source on an image plane by means of an erecting lens array.

FIG. 15B is a figure for showing a state of producing the unevenness inquantity of transmitted light.

FIG. 15C is a figure for showing a state of producing no unevenness inquantity of transmitted light.

FIG. 16 is a magnified view showing the arrangement of individual convexmicro-lenses within a circular area having a length of two times thelens pitch as its radius and having one convex micro-lens as its centeron a lens plate.

FIG. 17 is a magnified view showing point light source images formed onan image plane.

FIG. 18 is a sectional view showing an example of an image transferdevice for transferring a linear image to a linear image formation area,using an erecting lens array.

FIG. 19 is a sectional view showing another example of an image transferdevice.

FIG. 20 is a sectional view showing a further example of an imagetransfer device.

FIG. 21 is a figure for explaining a state of forming an image on alinear solid-state image sensor.

FIG. 22 is a magnified view showing the arrangement of individual convexmicro-lenses within a circular area having a length of two times thelens pitch as its radius and one convex micro-lens as its center on alens plate.

FIG. 23 is a magnified view showing an image formed on a linearsolid-state image sensor in a linear image formation area.

FIG. 24 is a figure for explaining a state where a lens plate isprovided with a light absorbing film between lenses.

FIG. 25 is a figure for explaining a state where a light absorbing filmis provided between lenses arranged in the hexagonal close-packedarrangement.

FIG. 26 is a figure for explaining an example of the arrangement oflight absorbing films.

FIG. 27 is a figure for explaining a state where a lens plate isprovided with a light shading wall between lenses.

FIG. 28A is a figure showing an example of the shape of a light shadingwall in the planar direction of a lens plate.

FIG. 28B is a figure showing an example of the shape of a light shadingwall in the planar direction of a lens plate.

FIG. 28C is a figure showing an example of the shape of a light shadingwall in the planar direction of a lens plate.

FIG. 28D is a figure showing an example of the shape of a light shadingwall in the planar direction of a lens plate.

FIG. 28E is a figure showing an example of the shape of a light shadingwall in the planar direction of a lens plate.

FIG. 29 is a figure for explaining an example of the arrangement of alight shading wall.

FIG. 30 is a figure for explaining an example of the arrangement oflight shading walls.

FIG. 31 is a figure for explaining a state where a light shading wall isprovided above a lens plate.

FIG. 32 is a figure for explaining a state where a light shading grooveis provided between lenses.

FIG. 33 is a figure for explaining an example of the arrangement oflight shading grooves.

FIG. 34 is a figure for explaining an example of the arrangement oflight shading grooves.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first embodiment of the present invention is described with referenceto the drawings.

FIG. 1 is a plan view showing a lens plate for forming an erecting lensarray to be used in a projector for projecting a three-dimensional ortwo-dimensional image in space, an image projector for projecting animage onto a screen and an image transfer device for forming an image ona light receiving device or a photosensitive member, and FIG. 2 is asectional view taken along line A—A of FIG. 1.

A lens plate 1 has a plurality of rectangular grooves formed atspecified intervals in parallel with one another relative to theshort-side direction. A rectangular groove 3 has a high aspect ratio inwhich the depth of its opening is larger than its width. In this case, agroove is formed having a depth of about 4 times the width of itsopening and about 60% of the thickness of the lens plate 1. Therectangular groove 3 is preferably formed to a depth of ⅓ or more of thethickness of the lens plate 1.

A material for the lens plate 1 is preferably thermoplastic, high inlight transmittance and low in moisture absorbency. In this embodiment,the lens plate 1 is made of a cycloolefin-based resin. A material forthe lens plate 1 may be an acrylic-based resin.

The lens plate 1 has a plurality of lens rows of spherical convexmicro-lenses 2, arranged in parallel with one another along theshort-side direction. The lens rows of convex micro-lenses 2 are formedat specified intervals with each rectangular groove 3 between the lensrows. The shape of each convex micro-lens 2 is circular in a planardirection of the lens plate. The convex micro-lenses 2 are formed onboth faces of the lens plate 1 and are arranged so that the optical axesof the convex micro-lenses 2 coincide with each other at both faces.

In this embodiment, the shape of a convex micro-lens is spherical butcan be also be aspherical. In addition to a structure in which convexmicro-lenses are formed on both faces of a lens plate, a structure inwhich they are formed on one face of the lens plate is also conceivable.In case lens rows of convex micro-lenses are formed on one face of alens plate, rectangular grooves are preferably formed on the face havingthe lens rows of convex micro-lens or on an opposite face. When rows ofconvex micro-lenses are formed on both faces of a lens plate,rectangular grooves are preferably formed on at least one of the faceshaving the lens rows of convex micro-lens.

In this embodiment, lens rows of convex micro-lenses and rectangulargrooves are formed in the short-side direction of a lens plate (in adirection perpendicular to the long-side direction of the lens plate).However, the lens rows of convex micro-lenses and the rectangulargrooves may be arranged in parallel with each other and be formed in anoblique direction to the long-side direction of the lens plate.

A low-reflection film of a silica compound coat is formed on the surfaceof the lens plate 1. The low-reflection film is intended to reduce thereflectivity of the lens plate and can use a material being low inrefractive index than the lens plate. A fluorine-based resin film andthe like may be used in addition to a silica compound coat.

In order to prevent stray light from coming in from the other portionsthan lenses, a mask 4 and an aperture stop 5 composed of a lightabsorbing film are formed outside of lens formation areas of both facesof the lens plate 1 and on outer circumferential areas of convexmicro-lenses. The lens formation area refers to the area encompassed bymicro-lenses 2 in the long-side direction and the sort-side direction.

Further, a light absorbing film is also formed on the side faces and thebottom face of each rectangular groove 3. As described above, therectangular groove 3 is preferably formed to a depth of ⅓ or more of thethickness of the lens plate 1. Light inputted at an angle wider than afield angle of a lens out of the light obliquely inputted can thus beshaded by a light shading portion of a light absorbing film provided toa depth of ⅓ or more.

Next, a method for manufacturing a lens plate according to the presentinvention is described.

First, a resin plate that is to become a substrate for a lens plate ismade by an extrusion molding method or an injection molding method. FIG.3 shows a plan view and a side view of a resin plate made by anextrusion molding method.

A metal mold has a rectangular groove 3 inverted shape formed on it soas to be capable of molding the rectangular grooves 3 at the same timeas molding the resin plate. The resin plate 6 is molded so as to belarge enough to form a number of lens plates arranged in parallel.

Next, light absorbing films for preventing stray light are formed in therectangular grooves 3. A black resin paint containing carbon (resist,ink, etc.) for example is used for a light absorbing film. The formationof light absorbing films is performed by applying a black resist to thebottom face and side faces of the grooves 3. The application of theblack resist to the rectangular grooves 3 can be easily performed byutilizing a capillary phenomenon. FIG. 4 shows a plan view and a sideview of a resin plate 6 having light absorbing films in the rectangulargrooves 3.

Next, a large-size lens plate is formed having a number of lens platesformed in parallel by simultaneously forming convex micro-lens rows by ahot-embossing method on both faces of the resin plate 6 having the blackresist applied to the rectangular grooves 3. The hot-embossing method isa resin molding method of transferring the shape of metal molds to aresin plate by holding the heated resin plate between the metal molds.FIG. 5 shows a plan view and a side view showing a large-size lens plate7 having convex micro-lenses formed on both faces by the hot-embossingmethod.

FIG. 6A is a partial magnified sectional view showing a resin platebefore lens rows are formed on the resin plate by the hot-embossingmethod, and FIG. 6B is a partial magnified sectional view of a resinplate after lens rows have been formed on the resin plate by thehot-embossing method.

When lens rows of convex micro-lens are formed by a hot-embossing methodafter light absorbing films have been formed in rectangular grooves 3,the grooves are crushed and filled by heat and pressure and therebyblack light shading walls are formed inside a lens plate. That is tosay, spaces provided by the grooves are crushed to disappear. Thestrength as a lens plate is thus increased.

Next, a low-reflection film of a silica compound coat is formed on thesurface of the large-size lens plate 7 having a number of lens platesformed in parallel. The low-reflection film is intended to reduce thereflectivity of the lens plates and can also use for example, afluorine-based resin film in addition to the silica compound coat.

Light absorbing films for preventing stray light from being inputtedfrom portions other than the lenses are formed outside the lensformation areas on both faces of the lens plate and on the outercircumferential portions of the convex micro-lenses. A photo-reactivematerial, for example, a black resist containing carbon is used for thelight absorbing films, and a mask outside the lens formation area and anaperture stop on the outer circumferential portion of each convexmicro-lens are formed by a photolithography process. FIG. 7 shows a planview and a side view showing a large-size lens plate 7 having a blackresist applied to it.

Each of the processes up to this state are performed collectively in thestate of a large-size lens plate 7 having a number of lens plates formedin parallel.

Next, the large-size lens plate 7 is cut. FIG. 8 shows a plan view and aside view showing the state of a large-size lens plate being cut.Individual lens plates 1 are obtained by cutting the large-size lensplate 7 having a number of lens plates formed in parallel.

Next, an image transfer device using an erecting lens array formed bycombining lens plates according to the present invention is describedwith reference to the drawings. FIGS. 9A to 9D are figures showing anexample of an image transfer device using lens plates according to thepresent invention. FIG. 9A is a plan view, FIG. 9B is a sectional viewtaken along line B—B of FIG. 9A, FIG. 9C is a bottom view, and FIG. 9Dis a sectional view taken along line C—C of FIG. 9A.

An erecting lens array is formed by stacking two or more lens plates onone another, and in FIGS. 9A to 9D, an erecting lens array 8 is formedby stacking two of lens plate 1. Each lens plate 1 has convexmicro-lenses formed on both faces of it. The erecting lens array 8 ishoused in a partition wall structure 9 having a slit-shaped opening 10that is in parallel with the long sides direction of a rectangular lensformation area of lens plate 1. This partition wall structure 9 ispreferably made of a light absorbing material.

The width of the slit-shaped opening 10 of the partition wall structure9 is determined so as to be capable of sufficiently removing stray lightintroduced in the short-side direction of the rectangular lens formationarea.

As shown in FIGS. 9A to 9D, for example, it is preferable to formrectangular grooves on the reverse faces (exit faces) of the stackedfirst and second lens plates (four lens faces in total) to form theerecting lens array and to form light shading walls (light absorbingfilms) for preventing stray light in these rectangular grooves.

In this image transfer device, stray light appearing in the long-sidedirection of the rectangular lens formation area is effectively removedby rectangular grooves formed in the short-side direction of therectangular lens formation area of each of the lens plates forming theimage transfer device.

FIGS. 10A to 10D are figures showing another example of an imagetransfer device using lens plates according to the present invention.FIG. 10A is a plan view, FIG. 10B is a sectional view taken along lineD—D of FIG. 10A, FIG. 10C is a bottom view, and FIG. 10D is a sectionalview taken along line E—E of FIG. 10A. It is possible to moreeffectively remove stray light by providing a slit-shaped opening 10 atthe entrance side of an erecting lens array as shown in FIGS. 10A to10D.

FIGS. 11A to 11D are figures showing a further example of an imagetransfer device using lens plates according to the present invention.FIG. 11A is a plan view, FIG. 11B is a sectional view taken along lineF—F of FIG. 11A, FIG. 11C is a bottom view, and FIG. 11D is a sectionalview taken along line G—G of FIG. 11A. As shown in FIGS. 11A to 11D, aslit-shaped opening 10 may be provided at each of the entrance side andexit side of an erecting lens array.

In FIGS. 9A to 9D, FIGS. 10A to 10D and FIGS. 11A to 11D, in order toremove stray light, a partition wall structure 9 is provided with aslit-shaped opening 10 that is in parallel with the long side of thelens formation area, but as shown in FIG. 12A, a slit-shaped opening 10may be covered with a transparent member 11 of glass or the like, and asshown in FIG. 12B, a partition wall structure 9 may be provided with aopening in parallel with the long side of the lens formation area, theopening being covered with a transparent member 12 of glass or the likehaving a slit printed on it. By covering the opening with thetransparent member it is possible to prevent dust and the like fromsticking on the erecting lens array.

In a lens plate according to the first embodiment of the presentinvention, because portions high in light absorbency are formed ingrooves that are each formed between adjacent lens rows of convexmicro-lenses, and because each of these portions functions as a lightshading wall for removing stray light, it is possible to effectivelyremove stray light appearing in a direction perpendicular to thesegrooves.

Also, because a method for manufacturing a lens plate of the presentinvention forms convex micro-lenses on a resin plate having groovesformed in it, the spaces, provided by the grooves are crushed and filledby heat and pressure and thereby light shading walls come to be formedinside the lens plate. Therefore, the strength of the lens plate can beincreased.

Further, in an image transfer device of the present invention, becausestray light appearing in the long-side direction of a rectangular lensformation area is effectively removed by grooves formed in the lensplate and because stray light appearing in the short-side direction ofthe rectangular lens formation area is effectively removed by apartition wall structure, stray light from all directions can beeffectively removed.

Next, a second embodiment of the present invention is described withreference to the drawings.

FIG. 13 is a plan view showing a lens plate for forming an erecting lensarray to be used in an image transfer device for forming an image on alight receiving device or a photosensitive member, and FIG. 14 is asectional view taken along line H—H of FIG. 13.

A material for a lens plate 21 is preferably a material beingthermoplastic, high in light transmittance and low in moistureabsorbency. In this embodiment, a lens plate of 2.29 mm in thickness isformed out of a cycloolefin-based resin by an injection molding process.A material for the lens plate 21 may be an acrylic-based resin.

Convex micro-lenses 22 are each a spherical lens of 0.35 mm in lensdiameter and 0.66 mm in radius of curvature. The lenses 22 are arrangedhexagonally on lens plate 21 at intervals of 0.45 mm in a lens pitch,and are formed on both faces of the lens plate 21. The optical axes andarrangements of the convex micro-lenses 22, respectively, on both facescoincide with each other.

In this embodiment, the shape of a convex micro-lens is spherical butcan also be aspherical. In addition to a structure described in whichconvex micro-lenses are formed on both faces of a lens plate, astructure in which the lenses are formed on one face is alsoconceivable.

The direction of arrangement of convex micro-lenses is inclined at anangle of 15° with respect to the long-side direction of the lensformation area 24. Lens formation area 24 refers to the area encompassedby the convex micro-lenses 22 in the short-side direction and thelong-side direction. Since it is in the direction of arrangement oflenses that a ghost image appears, the direction of arrangement ofconvex micro-lenses and the long-side direction (main-scanningdirection) of the lens formation area are provided so as not to be thesame as each other.

An erecting lens array is formed by arranging at least two of such resinlens plates opposite to each other.

FIG. 15A shows a state in which a light beam outputted from one lightsource 35 (object to be read) passes through a light beam input enablingarea A (a possible area A of light incidence) of an erecting lens array32 having at least two lens plates 30 arranged opposite to each otherand enters a linear solid-state image sensor 38. Although illustrated asa single element, light source 35 is one element of an array of lightelements. The unevenness in quantity of transmitted light appears when awhole portion of one or more convex micro-lenses 31 is not contained ina light beam input enabling area A, as shown in FIG. 15B. However, theunevenness in quantity of transmitted light does not appear a wholeportion of one or more of convex micro-lenses 31 is contained in a lightbeam input enabling area A as shown in FIG. 15C. In FIG. 15A, therefore,in order to reduce the unevenness in quantity of transmitted light, alight beam input enabling area A in an erecting lens array 32 of a lightbeam outputted from a light source contains the whole portion of one ormore of convex micro-lenses. It has been determined that the angle ofincidence (angular aperture) is ±6°, the working distance is 6.9 mm andthe radius of a light beam input enabling area A in an erecting lensarray 32 of a light beam outputted from a light source is 0.73 mm. Inorder to reduce the unevenness in quantity of transmitted light, thearea of a light beam input enabling area (determined by the relationbetween the angle of incidence and the working distance of a lens) needsto be equal to or greater than the area of each individual lens withinthe light beam input enabling area.

It is preferable that the length in the long-side direction (length inthe main-scanning direction) of a lens formation area having convexmicro-lenses regularly arranged at intervals of specified lens pitch isequal to or greater than the length in the main-scanning direction of alight beam input enabling area of a light beam outputted from a lightsource. It is also preferable that the length in the short-sidedirection (length in the sub-scanning direction) of the lens formationarea is equal to or greater than the length in the sub-scanningdirection of the light beam input enabling area.

FIG. 16 is a magnified view showing the arrangement of individual convexmicro-lenses within a circular area having a radius of two times thelens pitch and one convex micro-lens as its center on a lens plate, andFIG. 17 is a magnified view showing point light source images 33 formedon an image plane.

When forming a point light source into an image on an image plane usingan erecting lens array having lens plates arranged opposite to oneanother, it is in the direction of arrangement of lenses that a ghostimage appears. The distance of a point at which a ghost image appears onan image plane from a point light source is determined by the lens pitchand working distance. In FIG. 16, within a circular area having a radiusof two times the lens pitch and one convex micro-lens as its center, thedirection of a straight line tying the centers of convex micro-lenses 31in the area is deviated by 15° from the long-side direction(main-scanning direction) of the lens array.

In case of arranging convex micro-lenses in a hexagonal arrangement, itis preferable that the direction of a straight line tying the centers oflenses within the above-mentioned area does not coincide with an angleof 0° (parallel), 30°, 60° or 90° (perpendicular) relative to thelong-side direction (main-scanning direction) of the lens array. It isparticularly preferable to make an angle of 15°.

In case of a rectangular arrangement in which convex micro-lenses arearranged in the shape of a matrix, a longer lens pitch of rectangularlyarranged lenses is set as the long pitch, a shorter one is set as theshort pitch, and within a circular area having a radius of ((longpitch)²+(short pitch)²)^(1/2) and one convex micro-lens as its center,the direction of a straight line tying the centers of convexmicro-lenses in the area is deviated from the long-side direction(main-scanning direction) of the lens array.

FIG. 18 is a sectional view showing an example of an image transferdevice for transferring a linear image to a linear image formation areaB using an erecting lens array as described above. An erecting lensarray 32 is formed by arranging two lens plates 30 opposite to eachother. The lens plates each have convex micro-lenses formed on bothfaces, and are housed in a partition wall structure 36 a having aslit-shaped opening 34 a that is in parallel with the long-sidedirection of the erecting lens array 32 and is provided at the imagepoint side of the erecting lens array 32. A linear solid-state imagesensor 38 having at least one row of CCD's arranged is provided in alinear image formation area B to which a linear image is transferred. Itis preferable that the size of an area occupied by the linearsolid-state image sensor 38 is equal to or greater than that of thelinear image formation area. The slit-shaped opening 34 a is preferablyas close as possible to the solid-state image sensor.

FIG. 19 is a sectional view showing another example of an image transferdevice, and an erecting lens array 32 is housed in a partition wallstructure 36 b having a slit-shaped opening 34 b formed at the objectpoint side. This is the same as FIG. 18 except that a slit-shapedopening is provided at the object point side. A ghost image can be moreeffectively reduced by arranging a slit-shaped opening within theworking distance at the object point side. It is preferable that theslit-shaped opening 34 b is as close as possible to a light source.

FIG. 20 is a sectional view showing a further example of an imagetransfer device, having an erecting lens array 32 housed in a partitionwall structure 36 c. The partition wall structure 36 c has a slit-shapedopening 34 a at the image point side and a slit-shaped opening 34 b atthe object point side. Partition wall structure 36 c is the same as FIG.18 or 19 except that slit-shaped openings are provided at the imagepoint side and object point side. As shown in FIG. 20, a slit-shapedopening may be provided within each of the working distance at theobject point side and the working distance at the image point side. Theslit-shaped opening 34 a is preferably as close as possible to asolid-state image sensor and the slit-shaped opening 34 b is preferablyas close as possible to a light source.

That is to say, the present invention is preferably provided with apartition wall structure having a slit-shaped opening for removing anunnecessary light beam within the object point side working distanceand/or the image point side working distance.

The sectional shape of the forefront of a slit-shaped opening has aslope as shown in FIGS. 18, 19 and 20. As shown in FIG. 19, thesectional shape of the forefront of a slit-shaped opening may be widerat the lens side. Preferably, the sectional shape is made more narrow atthe light incidence side like the slit-shaped opening 34 a provided atthe image point side of the partition wall structure shown in FIG. 20.It is enough that the angle of slope of the forefront of a slit-shapedopening is an angle providing no scattering in a range of exerting noinfluence upon an image formation, and, in particular, it is preferablyof an angle of 45° or less. A slit-shaped opening may be formed into onebody with a partition wall structure and may be also provided separatelyfrom it. The long-side direction of a slit-shaped opening is preferablyin parallel with the main-scanning direction of a linear image formationarea. The position and width of the slit is properly designed within arange corresponding where a ghost image of a linear image does notappear in a linear image formation area.

An image to be read is assumed to be a linear image in this case but maybe either a point image or a planar image. The slit is particularlyeffective in case of a planar image. For a point image and a linearimage, although preferable, a slit-shaped opening may be or may not beprovided at the object point side and image point side. In case of aplanar image, it is indispensable to provide a slit-shaped opening atthe object point side. It may or may not be provided at the image pointside, but it is preferably provided.

A partition wall structure having a slit-shaped opening preferably has alight absorbing function in its inner walls in order to remove a lightbeam reflected in an optical system. Alternatively, a partition wallstructure itself is preferably formed out of a light absorbing material.It is also, preferable to make a partition wall structure have a lightabsorbency by using a black partition wall material for the partitionwall structure and making the surface of the partition wall materialfinely textured.

The length in the short-side direction (length in the sub-scanningdirection) of a lens formation area of an erecting lens array is made tobe equal to or more than the length in the short-side direction (lengthin the sub-scanning direction) of a slit-shaped opening and the lengthin the short-side direction of the slit-shaped opening is made to beequal to or more than the length in the short-side direction (length inthe sub-scanning direction) of a solid-state image sensor.

In an exemplary embodiment, the length in the short-side direction of aslit-shaped opening is 0.5 mm and the length in the short-side directionof a lens formation area is 2.0 mm in consideration of the tolerance inalignment of the slit-shaped opening and the solid-state image sensor.

Further, the length in the long-side direction (length in themain-scanning direction) of a lens formation area of an erecting lensarray is made to be equal to or more than the length in the long-sidedirection (length in the main-scanning direction) of a slit-shapedopening and the length in the long-side direction of the slit-shapedopening is made to be equal to or more than the length in the long-sidedirection (length in the main-scanning direction) of a solid-state imagesensor.

The working distance of an erecting lens array is made to be equal to ormore than a slit depth. The working distance being from the lens face ofthe erecting lens array to the slit-shaped opening.

As a linear solid-state image sensor 38, a device having CCD's arrangedin one line can be used in case of transferring a monochrome linearimage and a device having CCD's arranged in three lines can be used incase of transferring a color linear image.

FIG. 21 is a figure for explaining a state of forming an image on alinear solid-state image sensor 38, FIG. 22 is a magnified view showingthe arrangement of individual convex micro-lenses 31 within a circulararea having a radius of two times the lens pitch and one convexmicro-lens as its center on an erecting lens array, and FIG. 23 is amagnified view showing image points formed on a linear solid-state imagesensor 38 in a linear image formation area and points at which a ghostimage appears.

In case of taking an image into a solid-state image sensor through anerecting lens array, in order to reduce the stray light entering thesolid-state image sensor, convex micro-lenses are arranged so that thedirection of arrangement of the convex micro-lenses and the long-sidedirection of the solid-state image sensor do not become the same as eachother.

In case of arranging convex micro-lenses in a hexagonal arrangement, thedirection of a straight line tying the centers of convex micro-lenses ismade so as not to become the same as the long-side direction of asolid-state image sensor in a circular area having a radius of two timesthe lens pitch and one convex micro-lens as its center.

In case of a rectangular arrangement, the direction of a straight linetying the centers of convex micro-lenses is made so as not to become thesame as the long-side direction of a solid-state image sensor within acircular area having a radius of ((long pitch)²+(short pitch)²)^(1/2)and one convex micro-lens as its center.

As described above, it is necessary that at least the long-sidedirection of a solid-state image sensor and the direction of arrangementof convex micro-lenses do not coincide with each other in a circulararea having a radius of two times the lens pitch and one convexmicro-lens as its center in case of arranging convex micro-lenses in ahexagonal arrangement and in a circular area having a radius of ((longpitch)²+(short pitch)²)^(1/2) and one convex micro-lens as its center incase of a rectangular arrangement. Furthermore, in the above-describedareas, it is necessary that a ghost image is not formed in an area ofthe solid-state image sensor, namely, that half the length in theshort-side direction of the solid-state image sensor is shorter than theshortest distance from the center line along the long-side direction ofthe solid-state image sensor to an image point at which a ghost imageappears.

In a manufactured image transfer device, the result of taking an imageinto a solid-state image sensor for the combination of a linear image,an erecting lens array, a slit and the solid-state image sensor hasshown that stray light is so slight that it is impossible to distinguishbetween the influences of quantizing noise and stray light.

Examination of image formation characteristics of a point light sourcehas shown that the quantity of stray light at a location where asolid-state image sensor is to be installed has been reduced to 2/1000.

FIG. 24 is a figure for explaining a state of providing a lightabsorbing film (light shading film) 40 between lenses of 0.35 mm in lensdiameter arranged at intervals of 0.45 mm in lens pitch on a lens plateand FIG. 25 is a figure for explaining a state of providing a lightabsorbing film (light shading film) 40 between lenses of 0.45 mm in lensdiameter arranged at intervals of 0.45 mm in lens pitch in the hexagonalclose-packed arrangement (arranged in contact with one another).

Assuming that lens faces of lens plates forming an erecting lens arrayare face [1], face [2], face [3], . . . , face [N], respectively, in anorder from the light source entrance side, each face corresponding to aneven number is preferably provided with a light absorbing film 40. Eachface corresponding to an of odd number may or may not be provided withthe light absorbing film 40, but is preferably provided. FIG. 26 is afigure for explaining an example of arrangement of light absorbing filmsin case of having lens faces of faces [1] to [4].

When using an erecting lens array having at least two lens platesarranged opposite to each other as an optical system, when it is assumedthat a perpendicular line from a solid-state image sensor (CCD) to alens face is an optical axis, the solid-state image sensor also has alight beam (stray light) other than the light beam emitted from anobject point on the optical axis inputted into it.

This stray light depends on the arrangement (direction and pitch) andangular aperture of the erecting lens array. A greater amount of straylight enters from a direction in which the lens pitch is smaller. Whenthe angular aperture is made smaller, stray light comes to enter from apart closer to the optical axis. Stray light from a part closer to theoptical axis has a greater influence on an image, whereas stray lightmore distant from the optical axis has a smaller influence on the image.

In order to obtain a good image formation performance by an erectingunit magnification optical system, stray light must be removed by somemethod. An image transfer device of the present invention removes thestray light from a part relatively close to the optical axis by aslit-shaped opening and removes the stray light from a part distant fromthe optical axis by a light shading film provided between lenses on alens plate.

In case that the angular aperture of lens is wide, an angle causing aghost image to appear is only a wide angle and since it is enough toremove only a ghost image in a wide angle range, it is possible toremove a ghost image by means of only light shading films. On the otherhand, in case that the angular aperture of lens is narrow, an anglecausing a ghost image to appear ranges from a narrow angle to a wideangle and light in a wide range enters a solid-state image sensor andtherefore, it is preferable to remove a ghost image in a narrow anglerange by a slit-shaped opening and a ghost image in a wide angle rangeby light shading films. Accordingly, in case of a narrow angularaperture, it is preferable to provide both a slit-shaped opening andlight shading films. For example, in case of an angular aperture of 10°,light shading films may be enough but in case of an angular aperture of6°, it is preferable to provide both a slit-shaped opening and lightshading films.

In case that a slit-shaped opening cannot be provided for reasons suchas device design, it is possible also to obtain an almost equivalenteffect to a slit by making the height of each light shading film higher.

FIG. 27 is a figure for explaining a state of providing a light shadingwall between lenses on a lens plate. It is preferable to provide lightshading walls 50 of light absorbency on at least one lens plate.

Light shading walls of 0.35 mm in aperture diameter, 0.42 mm in pitchand 0.2 mm or more in height (height from the vertex of a lens to thetop of a light shading wall) are provided on individual lenses of 0.35mm in lens diameter and 0.42 mm in lens pitch. Because an angle θ madebetween a light beam entering the vertex of a lens and the optical axisof the lens is made to be 45° or less by providing such light shadingwalls, it is possible to remove a light beam making an angle greaterthan 45° with the optical axis of lens, namely, the stray light from apart distant from the optical axis. Because, the angle of incidence ofstray light varies according to the angular aperture of lens, it isenough to properly design the height of a light shading wall in relationto the angular aperture of lens. The height is preferably 0.15 to 2.0 mmand more preferably 0.2 to 2.0 mm.

It is conceivable that the shape of a light shading wall in the planardirection of a lens plate is rectangular as shown in FIG. 28A, hexagonal(honeycomb-shaped) as shown in FIG. 28B, circular as shown in FIG. 28C,or shapes where all parts except lenses are formed as a light shadingwall as shown in FIG. 28D and FIG. 28E. In case of assuming that lensfaces are face [1], face [2], face [3], . . . , face [N], respectively,in an order from the light source entrance side, it is preferable toprovide light shading wall 50 on face [1].

In case of providing both of light shading wall 50 and light absorbingfilm 40, light shading wall 50 is desirably provided on face [1] that isclosest to the light source entrance side and light absorbing film 40 isdesirably provided on face [N] that is most distant from the lightsource entrance side. As for faces between face [1] and face [N], eitherof face [2M (M=1, 2, 3, . . . )] or face [2M+1] is provided with lightabsorbing film 40. Light absorbing film 40 on face [N] may be replacedwith light shading wall 50. FIG. 29 is a figure for explaining anexample of arrangement of light shading wall 50 and light absorbing film40 in case of the existence of lens faces [1] to [4], and FIG. 30 is afigure for explaining an example of arrangement in case of replacinglight absorbing film 40 of face [4] with light shading wall 50. A lightshading wall may be formed out of the same material as a light absorbingfilm.

FIG. 31 is a figure for explaining a state of providing a light shadingwall above a lens plate. Even when a light shading wall 50 is above thelens plate without being in contact with a lens plate, a similar effectcan be obtained. When a light shading wall is not in contact with a lensplate, the pitch of lenses and the pitch of light shading walls may bedifferent from each other. When a light shading wall is not in contactwith a lens plate, because light is inputted from a wider angle range, ahigher light shading wall is required than when both of them are incontact with a lens plate (at least double or more height is required).When both of them are not in contact with each other, because a problemof moiré occurs, both of them are preferably in contact with each other.

When the height of a light shading wall is several hundred microns ormore, depending upon the light transmittance and the lens angularaperture of an erecting unit magnification optical system, because straylight distant from the optical axis as well as stray light close to theoptical axis can be removed, a good image can be obtained even when theabove-described partition wall structure is not provided with aslit-shaped opening.

Next, making a light shading wall is described. A first embodiment formaking a light shading wall forms a light shading wall by means of athick film printing process. First, a photosensitive black resin paint(ink or resist) is applied to a resin base material to a specifiedthickness (20 to 100 μm) and is dried until the stickiness of thesurface disappears. The drying is performed at a temperature not higherthan the softening temperature of the resin base material.

A marker is installed outside a print-patterning area and then exposureis performed using a mask. By repeating these processes, the black resinpaint is stacked up to a desired thickness. Next, development andpost-cure (hardening by heating) are performed. In this embodiment, thethickness obtained by performing the process is 70 μm and a wall of 210μm is formed by repeating the process three times. The surface of theblack resin is preferably pear-skin (textured) in order to reduce asurface reflection. Particularly the inner wall is preferably pear-skin.

A second embodiment for making a light shading wall forms a lightshading wall by forming a black resin rib. First, a black resin rib ismade by an injection molding process according to the followingprocedure. A plate like pinholder having rod-like projections and a pairof metal molds consisting of a multi-hole plate having holescorresponding to the projections and a flat plate are used in molding.First, this embodiment places the multi-hole plate on the pinholder-likeplate While inserting the projections of the pinholder-like plate intothe holes of the multi-hole plate, and further places the flat platethereon.

Next, resin is injected through many pin gates provided in the flatplate. The space between the multi-hole plate and the flat plate isfilled with the resin and is cooled. After being cooled, the flat plateis detached and then a molded product is exfoliated from thepinholder-like plate. When making the inner wall pear-skin, it is properto provide a draft angle of 10° or less in order to facilitate amold-releasing action after molding. The obtained molded product isplaced on a lens plate to form a lens array with a light shading wall.

When providing a draft angle to a projection, stray light can beefficiently removed by arranging the thinner side of a resin rib at thelens side. The quantity of transmitted light is increased by arrangingthe thicker side of the resin rib at the lens side. The shape of holesof a resin rib may be hexagonal (honeycomb-shaped), rectangular,circular or any shape.

In both of the first and second embodiments, it is desirable that thecoefficient of thermal expansion of resin used in a light shading wallis close to that of resin used in a lens. The coefficient of thermalexpansion is preferably on the order of 10⁻⁵(1/° C.).

In addition to the first and second embodiments, a rib can be also madeby making holes in a black film or the like having a specified thicknessby means of an ultraviolet laser beam.

FIG. 32 is a figure for explaining a state of providing a light shadinggroove between lenses of 0.35 mm in lens diameter and 0.45 mm in lenspitch. It is preferable to provide a light shading groove 60 betweenlenses on one face or both faces of at least one lens plate in order toremove an unnecessary light beam. A deeper light shading groove is morepreferable, and the depth of the groove is preferably 30% or more of thethickness of a lens plate, more preferably 50% or more, and mostpreferably 60% or more.

In case of assuming that lens faces are face [1], face [2], face [3], .. . , face [N], respectively, in an order from the light source entranceside, a light shading groove is provided on a face having an odd numberor an even number. FIG. 33 is a figure for explaining an example ofarrangement of light absorbing films when providing light shadinggrooves on faces of odd numbers out of faces [1] to [4]. When providinglight shading grooves on faces of odd numbers, light absorbing film 40is desirably provided on face [N] being most distant from the lightsource entrance side, and a light absorbing film may or may not beprovided on the other faces of even numbers other than face [N]. FIG. 34is a figure for explaining an example of arrangement of light absorbingfilms when providing light shading grooves on faces of even numbers outof faces [1] to [4]. When providing light shading grooves 60 on faces ofeven numbers, light absorbing film 40 is desirably provided on face [1],and a light absorbing film may or may not be provided on the other facesof odd numbers other than face [1].

In FIGS. 33 and 34, light shading film 40 may be replaced with lightshading groove 60, and light shading grooves 60 may be provided on allfaces.

And in the above-described embodiments, in order to remove a light beamof unnecessary wavelength from entering a solid-state image sensor, anultraviolet cutoff function or an infrared cutoff function may beprovided in a lens plate, or an ultraviolet cutoff filter or an infraredcutoff filter may be provided in an optical path.

With respect to the combination of a slit-shaped opening, a lightshading film, a light shading wall and a light shading groove, one ofthe most preferable combinations is a combination of a slit-shapedopening, a light shading film and a light shading wall (or light shadinggroove) provided on face [1] closest to the light source entrance side(hereinafter, referred to as combination (1)). In case of providinglight shading films on all faces other than face [1], it is possible toremove a ghost image at all lens angular apertures. A light shading wallor a light shading groove may be used in place of a light shading film.Another preferable combination is the combination of a light shadingfilm and a light shading wall (or a light shading groove) provided onface [1] closest to the light source entrance side (hereinafter,referred to as combination (2). This combination is preferable in caseof a wide angular aperture. A light shading wall or a light shadinggroove may be used in place of a light shading film. It is preferablethat each of combination (1) and combination (2) is provided with apartition wall structure having an erecting lens array housed in it.

Because an erecting lens array according to the second embodiment of thepresent invention is formed so that the direction of arrangement ofconvex micro-lenses and the long-side direction of a lens formation areaare not the same as each other, it can sufficiently remove stray light.

Because an image transfer device according to the second embodiment ismade so that the long-side direction of a solid-state image sensor andthe direction of arrangement of lenses are not the same as each otherand no ghost image is formed in the area of the solid-state imagesensor, a ghost image can be sufficiently removed.

1. A lens plate comprising; a rectangular plate having a plurality ofgrooves formed to a specified depth at specified intervals in parallelwith one another in the short-side direction of the plate, a pluralityof lens rows of convex micro-lenses, said lens rows being formed withsaid grooves between them at specific intervals in parallel with oneanother in the shot-side direction of the plate on said plate, and lightabsorbing films formed in said grooves, wherein the grooves extendcontinuously across multiple convex micro-lenses in the short-sidedirection.
 2. A lens plate according to claim 1, wherein; in case thatthe lens rows of said convex micro-lenses are arranged on one face ofsaid plate, said grooves are formed on a face on which the lens rows ofsaid convex micro-lenses are formed or a face opposite to that face, andin case that the lens rows of said convex micro-lenses are arranged onboth faces of said plate, said grooves are formed on at least one of thefaces on which the lens rows of said convex micro-lenses are formed. 3.A lens plate according to claim 1, wherein; said grooves are formed to adepth of ⅓ or more of the thickness of said plate.
 4. A lens plateaccording to one of claims 1 to 3, wherein; said plate is formed out ofresin.